JPS5939111A - Amplifier - Google Patents

Abstract

PURPOSE:To obtain an amplifier possible for operation at a low voltage, by generating a current equivalent to a base current of the 1st transistor(TR) impressed with the 1st constant current with the 2nd constant current and an output of a current mirror circuit and impressing the equivalent current to the 2nd TR. CONSTITUTION:The 1st constant current source 25 is connected to a base of the 1st TR21 and an input of the current mirror CM comprising TRs 22, 23, and the 2nd constant current source 26 is connected to a base of the 2nd TR20 and an output of the CM. Further, constant current sources 24, 27 having equal current value Ic are connected to a collector of the TRs 21, 20. A collector current IM of the TR22 is expressed as IM=Ir-Ic/hFE, where Ir is a current value of both the current sources 25, 26 and hFE is the DC current amplification factor of the TRs 21, 20, and the IM becomes an output current of the CM with the TRs 22, 23 taken as the same characteristic, and the base current of the TR20 is Ir-IM=Ic/hFF. Thus, the base current of the TR20 is decreased and operated at a low power supply voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an amplifier device which can reduce the apparent input bias current of a transistor circuit and can operate at a low voltage.

Conventional Structure and Problems The Darlington connection is well known as a method of reducing the base current of a conventional transistor.

Figure 1 shows an example of using a Darlington connection in the input stage of an operational amplifier. Transistor (first
The base current of the transistor (corresponding to transistor 6 in the figure) flows through a resistor connected externally to the input terminal, thereby generating an input voltage offset and causing an error in the output signal. Therefore, the value of the external resistance cannot be increased. However, in general, there is a degree of freedom in external connection conditions,
Furthermore, in order to eliminate errors in the output signal, it is desirable that the base current at the input terminal be as small as possible.

In the conventional example shown in FIG. 1, transistors 6 and 7. Transistors 8 and 9 are each configured as a Darlington-connected differential amplifier. Here 1
0 is a constant current source that determines the emitter current of the differential amplifier, 11
and 12 are current mirror transistors that constitute the load of the differential amplifier, 13 is a transistor in the second amplification stage driven by the output of the differential amplifier, and 14 is a constant current source that determines the collector current of the second amplification stage. , 3 is an output terminal, 4 is a positive power supply terminal, and 6 is a negative power supply terminal.

Looking at the minimum operating voltage of this circuit, we can see that from the positive power supply terminal 4 to the constant current source 10. In the current path from the emitter base of the transistor 6 to the negative input terminal 1 via the emitter base of the transistor 7, there are two pace emitter voltages and the voltage of one constant current source. The pace emitter voltage is vBE.

When the constant current source is configured with a current mirror of transistors, the minimum operating voltage is vCESAT, so
The minimum power supply voltage required for this circuit to operate is 2■
BE+■cEsAT. Generally, vBE is about 0.
7v, vcEsAT is approximately o, 2v, so the minimum operating voltage of this circuit is 2XO7+0.2=1.6 (volts). This voltage can be used with two (3) dry batteries, but in order to extend the battery life, an amplifier device that can operate stably even with a lower power supply voltage is desired.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an amplifier device that has a lower base current than the conventional example and operates at a lower power supply voltage.

Structure of the Invention The present invention provides a first constant current source connected to the base of a first transistor and an input of a current mirror, and a second constant current source having a predetermined current ratio with respect to the first constant current source. A source is connected to the base of the second transistor and the output side of the current mirror, and a current equivalent to the base current of the first transistor is connected to the difference between the second constant current source and the output side current of the current mirror. This amplification device is configured to generate a large amount of energy and supply it to the base of the second transistor, and is capable of operating at a low voltage.

DESCRIPTION OF THE EMBODIMENT FIG. 2 shows the configuration of an embodiment of the present invention. A first constant current source 26 is connected to the base of the first transistor 21 and the collector of the transistor 22 which is input to the current mirror composed of the transistors 22 and 23;
A second constant current source 26 is connected to the base of the second transistor 20 and the collector of the transistor 23 which is the output of the current mirror. Furthermore, the first transistor 21
A constant current source 24 is connected to the collector of the second transistor 20, and a constant current source 27 is connected to the collector of the second transistor 20.
The current values of 7 are the same. Here, the currents of the first and second constant current sources 25 and 26 are both Ir.

The currents of constant current sources 24 and 27 are both ■. The DC current amplification factor of each transistor is hFE, and transistor 2
Letting the collector current of 2 be IM, the following equation (1) holds true.

Here, if transistors 22 and 23 have the same characteristics, the collector current of transistor 23 is equal to the collector current of transistor 22, so the current flowing into the base of transistor 2o is Ir-IM, and if 2o and 21 have the same characteristics, then this The value is equal to the relationship between the collector current and the base current of transistor 20. Therefore transistor 2
The base current of o is supplied by the current (I, -IM) generated by the difference between the current lr of the second constant current source 26 and the output current IM of the current mirror. - Fig. 3 shows a circuit diagram of an embodiment in which the present invention is applied to an operational amplifier. The configuration shown in FIG. 2 is used for each of the first block 68 and the second block 69. Other parts are the same as the conventional example. A constant current source 41 (corresponding to the constant current source 10 in FIG. 1) determines the emitter current of a differential amplifier consisting of transistors 39 and 40, and transistors 42 and 43 are loads of the differential amplifier and are connected in a current mirror type. has been done. A transistor 64 (corresponding to transistor 13 in FIG. 1) driven by the output of the differential amplifier is a second amplification stage, and determines the collector current by a constant current source 63 (corresponding to 14 in FIG. 11).

Further, 66 is an output terminal, 66 is a positive power supply terminal, and 67 is a negative power supply terminal.

First, the first block 68 will be explained. In this embodiment, the base of the first transistor 31 and the collector of the transistor 33, which is the input of the current mirror, are connected to the base of the first transistor 31.
The transistor 34 is connected to the constant current source 36 of the transistor 34 and is the output of the current mirror with the base of the second transistor 39.
, and the collector thereof are connected to a second constant current source 37.

The current value of the constant current source 3o is set to be equal to the emitter current of the transistor 39 and % of the constant current source 41. By doing this, the transistor 39
The base current is supplied by the difference between the currents of the second constant current source 37 and the transistor 34 which is the output of the current mirror. Here, as the diode 32, a diode whose forward voltage is equal to the collector-emitter voltage of the transistor 42 is used,
By setting the voltage of the constant voltage source 36 to a value obtained by subtracting the pace emitter voltage of the transistor 33 from the base voltage of the transistor 39, the emitter voltage of the transistor 31 is made equal to the emitter voltage of the transistor 39. In this way, the collector-emitter voltages of transistor 31 and transistor 39 can be made equal, and transistor 3
hFE due to the Early effect of 1 and transistor 39
It is possible to prevent a change in the current from causing an error in the base current of the transistor 39.

The second block 69 has the same configuration as the first block 68 and therefore operates in exactly the same way.

The constituent elements are transistors 40, 45, 46, and 61;
4B, 49.50 is constant current source, 62 is diode, 47
is a constant voltage source.

As described above, the base current of the transistor 39, the base current of the transistor 39, and the base current of the transistor 4° are absorbed by the difference current between the constant current source 37 and the transistor 34, and the difference current between the constant current source 48 and the transistor 46, respectively. Therefore, the negative input terminal 38. No current flows into or out of the external resistor connected to the positive input terminal 44. In other words, there is no apparent input bias current. Therefore, even if a large resistance value is used as an external resistor, no input voltage offset will occur, and this will not cause an error in the output signal. Furthermore, in the conventional example shown in FIG. 1, transistors 6 and 7 and transistors 8 and 9
However, in the embodiment of FIG. Only the relative variations in voltage affect the output voltage offset. Therefore, in this circuit, the number of elements that require relative balance is reduced, and productivity is improved.

Still looking at the minimum operating voltage of this circuit, the positive power supply terminal 66
Among the paths through which current flows from the positive power supply terminal 56 to the negative power supply terminal 67, the path with the highest minimum operating voltage is from the positive power supply terminal 56 to the constant voltage source 36. This is a path leading from the transistor 33 to the negative power supply terminal 67 via the constant current source 36. In order to examine the minimum operating voltage in this path, a specific configuration of the constant voltage source 36 and constant current source 36 in FIG. 3 is shown in FIG. 4.

In FIG. 4, 31a, 33a, 34a.

39a, 6ea, 57a are 31.33°3 in Figure 3.
It is the same as 4.39 and 56.57. Constant voltage source 36 and constant current source 36 in FIG. 3 correspond to constant voltage block 69 and transistor 66 in FIG. 4, respectively. The operation of the configuration shown in FIG. 4 will be explained below. The value R61 of the resistor 61 connected to the transistor 630 pace
The emitter-collector voltage vcE63 of the transistor 63 is determined by the value R62 of the resistor 62, and when the base-emitter voltage of the transistor 63 is vBEea, the relational expression becomes equation (2).

Generally, the emitter-to-pace voltage of a transistor can be regarded as a substantially constant voltage, so from equation (2), vCE63 becomes a constant voltage source. Here, the constant current source 64 sinks the base current of the transistor 63.

Looking at the minimum operating voltage of vcE63, transistor 63
Since the relationship in equation (2) holds unless saturated, the collector-emitter saturation voltage vCESAT of the transistor 63
63 can be considered to be the minimum operating voltage.

Next, let's look at the transistor 66 that constitutes the constant current source. transistor 66, transistor 66, transistor 6
7 constitutes a general current mirror, and if the characteristics of each transistor are the same, a current equal to the current value of constant current source 68 flows through transistors 65 and 66. At this time, the lowest operating voltage of the transistor 65 is the lowest operating voltage of the transistor 65.
The collector-emitter saturation voltage vCESAT66 rises.

Consider again the path for determining the minimum operating voltage of the circuit shown in FIG. The minimum operating voltage of each element existing in the path is determined by the constant voltage source 36 vcEsAT63. Transistor 33 (33
a) is the pace emitter voltage ■BE331 Constant current source 3
6 is vCESAT66 and vCESAT63
CESATss is vCESAT, which is the collector-emitter saturation voltage of a general natra7 transistor, and vBE33 is vB, which is the pace-emitter voltage of a general transistor.
E, then add all the villages (1vBE+2vc
EsAT). This is the minimum operating voltage for this circuit. That is, in a typical element, the voltage is 1.1V, which can be significantly lower than the conventional example of 1.6V.

Effects of the Invention As described above, the present invention makes it possible to reduce the apparent input bias current and also enables low voltage operation. Furthermore, by incorporating the present invention into an IC, the relative accuracy of each element can be improved, and the base current can be reduced, which greatly contributes to the rationalization and high reliability of the system, which are the features of IC implementation. be.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional amplifier device, Figure 2 is a configuration diagram of an embodiment of the present invention, Figure 3 is a circuit diagram of a device to which the present invention is applied, and Figure 4 is the constant voltage of Figure 3. source 36 and constant current source 36
FIG. 20...°...second transistor, 21...
・First transistor, 22.23... Transistor forming a current mirror, 25... First constant current source, 26... Second constant current source, 24
, 27.41... constant current source, 42.43...
...A transistor that constitutes a current mirror. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (2)

[Claims] (1) A first constant current source is connected to the base of the first transistor and the input of the current mirror, and a second constant current source having a current ratio of a predetermined ratio to the first constant current source is connected to the first constant current source. Connected to the base of transistor No. 2 and the output of the current mirror,
A current equivalent to the base current of the first transistor is
An amplifying device characterized in that the amplifier is configured to generate a current based on a difference between an output current of a constant current source and a current mirror, and to supply the generated current to the base of a second transistor. (2) The amplifier device according to claim 1, wherein the potential difference between the collector and emitter of the first transistor is made equal to the potential difference between the collector and emitter of the second transistor.